This application relates to the art of ultra thin films and, more particularly, to such films that are formed of amphiphilic molecules. The invention is particularly applicable to a method of applying such films to substrate surfaces and will be described with specific reference thereto. However, it will be appreciated that certain features of the invention have broader aspects, and may be used in other methods as well as for other purposes.
Polymerizable amphiphilic molecules having the intrinsic ability to self-assemble in a thin film are well known. By way of example, descriptions of such materials and their ability to form thin films are contained in: W. C. Bigelow et al, J. Colloid. Sci., 1, 513-538 (1946); L. H. Lee, J. Colloid. & Interface Sci., 27, 751-760 (1968); E. E. Polymeropoulos et al, J. Chem. Phys., 69, 1836-1847 (1978); and J. Sagiv, U.S. Pat. No. 4.539,061, issued Sep. 3, 1985. The disclosures of which are hereby incorporated herein by reference. These publications disclose compositions that include solvents in which a film forming substance is soluble, and the solvents usually are toxic and environmentally unfriendly. Highly liquid compositions also lose their usefulness very rapidly when exposed to airborne moisture because the amphiphilic molecules are highly reactive with water and tend to form molecular agglomerations that precipitate out of the solution.
Compositions and methods for use in applying ultra thin films of self-assembling amphiphilic molecules to substrate surfaces are described in our commonly assigned U.S. Pat. Nos. 5,078,791; 5,106,561; 5,166,000; 5,173,365; 5,204,126; 5,219,654 and 5,300,561, the disclosures of which are hereby incorporated herein by reference. These compositions and methods are advantageous for providing ultra thin films on porous and non-porous surfaces of such materials as glass, ceramic, porcelain, fiber glass, metals and plastics. The film serves one or more of a variety of purposes including scratch resistance, corrosion protection, protection for anti-reflective coatings on lenses, friction reduction, print priming, moisture barriers, and the like. For example, the films may be used for coating laboratory glassware and for providing a non-stick coating for pots, pans, dishes or utensils. These films are particularly advantageous for use on anti-reflective glass and plastic lens surfaces, including plastic eyewear lenses manufactured from CR-39 (trademark of PPG Industries), polycarbonate and high index resins that are pre-treated with a hard coat for scratch resistance.
The gas phase reaction of different amphiphilic organosilanes with a silica surface in vacuum cell has been reported by a number of authors: J. Phys. Chem 70, 2937 (1966); Trans. Faraday. Soc., 63, 2549 (1967); J. Phys. Chem., 73, 2372 (1969); Langmuir, 7, 923 (1991). The disclosures of which are hereby incorporated herein by reference. Commercial hydrophobic fumed silicas such as Aerosil R 972 from Degussa Corp. and Cab-O-Sil TT-610 from Cabot Corp. are produced using dichlorodimethylsilane by gas phase reactions. Recently, others have also reported the formation of hydrophobic silica using other amphiphilic alkylsilanes in a gas phase reaction inside a vacuum cell: Langmuir, 9, 3518 (1993); Langmuir, 13, 1877 (1997). The disclosures of which are hereby incorporated herein by reference. The reactions reported in these articles were performed to coat silica at very high temperatures in the range of 200-300.degree. C. or higher. A lower temperature inside the cell results in the absence of any coating on the silica surface because the molecules used in the process require a high temperature for achieving a thermal reaction. Also, the process requires steam hydration followed by dehydration at a high temperature of 400.degree. C. or above along with degassing. The apparatus and the process are limited to preparation of small samples of the coated material because an extremely strong vacuum is required and the vacuum cell is small.
The use of prior compositions and methods to form a film on a substrate surface leaves excess composition on the surface that must be removed. Disposal of this excess material is difficult, and it is difficult to remove from the excess material from irregular surfaces. Large articles and surfaces with microstructures are difficult to coat when using prior compositions and methods, and the process is very slow. Prior methods require large quantities of coating composition that usually is obtained by repeatedly removing smaller quantities from one open container so that vigilance is necessary to prevent contamination of the composition and exposure to moisture.
It would be desirable to have a process for applying hydrophobic thin films of amphiphilic molecules to different surfaces in a manner that is very fast and cost effective. It would also be desirable to have a process that could be used to coat substrate surfaces of any size or shape without requiring removal of excess coating composition and disposal of same.